Unit 7 - Magnets & Electromagnetism

Question 1

At which part of a magnet are the
magnetic forces strongest?

Answer 1

The poles of the magnet.

Question 2

What happens when two magnets are
brought close to each other?

Answer 2

They exert a force on each other.

Question 3

What type of force is exerted if two like
poles of a magnet are brought near each
other?

Answer 3

A repulsive, non-contact force.

Question 4

What type of force is exerted if two unlike
poles of a magnet are brought near each
other?

Answer 4

An attractive, non-contact force.

Question 5

What is the difference between a
permanent magnet and an induced
magnet?

Answer 5

● A permanent magnet produces its own
magnetic field
● An induced magnet becomes magnetic
when placed in a magnetic field

Question 6

What type of force does induced
magnetism always cause?

Answer 6

A force of attraction.

Question 7

What happens when an induced magnet
is removed from a magnetic field?

Answer 7

The induced magnet loses most/all of its
magnetism.

Question 8

What is a magnetic field?

Answer 8

The region surrounding a magnet where
another magnet or magnetic material
experiences a non-contact force.

Question 9

Give four examples of magnetic
materials

Answer 9

1. Iron
2. Steel
3. Cobalt
4. Nickel

Question 10

What can always be said about the force
between a magnet and a magnetic
material?

Answer 10

It is always attractive.

Question 11

How does the strength of a magnetic
field alter as you move further away from
the magnet producing it?

Answer 11

The magnetic field strength decreases
the further you move away.

Question 12

In what direction does a magnetic field
point?

Answer 12

● In the direction that a north pole would
experience a force if placed in the field
● From the north seeking pole to the
south seeking pole of a magnet

Question 13

What does a magnetic compass
contain?

Answer 13

A small bar magnet that points in the
direction of the Earth’s magnetic field.

Question 14

What is produced when current flows
through a conducting wire?

Answer 14

A magnetic field is produced around the
wire.

Question 15

What determines the strength of the
magnetic field around a current-carrying
wire?

Answer 15

● The magnitude of the current flowing
through the wire
● The distance from the wire

Question 16

What is a solenoid?

Answer 16

A coil of wire which when current passes
through creates a strong magnetic field.

Question 17

Describe the magnetic field found inside
a solenoid.

Answer 17

Strong and uniform.

Question 18

What is an electromagnet?

Answer 18

● A solenoid with an added iron core
● Adding the iron core increases the
strength of the magnetic field

Question 19

What is the motor effect?

Answer 19

When a force is exerted between a
magnetic field and a current-carrying
conductor placed in that field.

Question 20

What rule is used to determine the force
experienced due to the motor effect?

Answer 20

Fleming’s Left-Hand Rule

Question 21

When using Fleming’s left hand rule
what does the forefinger represent?

Answer 21

The forefinger points in the direction of
the magnetic field.

Question 22

When using Fleming’s left hand rule
what does the second finger represent?

Answer 22

The second finger points in the direction
of current flow in the conductor.

Question 23

What factors affect the size of the force
on a current-carrying wire in a magnetic
field?

Answer 23

● The magnitude of the current flowing
through the conductor
● The strength of the magnetic field that
the conductor is placed in

Question 24

If the direction of current in a
current-carrying wire placed in a uniform
magnetic field is reversed, what happens
to the force?

Answer 24

The direction of the force is reversed.

Question 25

If the strength of the current in a
current-carrying wire placed in a uniform
magnetic field is increased, what
happens to the force?

Answer 25

The strength of the force is increased.

Question 26

What criteria must be met for the
equation linking force, magnetic flux
density, current and length to hold?

Answer 26

The conductor must be at right-angles to
the magnetic field it is placed in.

Question 27

What is the unit used for magnetic flux
density?

Answer 27

Tesla, T

Question 28

How does an electric motor work?

Answer 28

● A coil of wire, carrying a current, is placed in a magnetic field
● The forces on the two sides perpendicular to the field experience forces in opposite directions
● This causes a rotational effect

Question 29

How do loudspeakers make use of the
motor effect?

Answer 29

The motor effect is used to convert
variations in the current of an electrical
circuit into the pressure variations which
produce audible sound.

Question 29

Explain how a loudspeaker works.

Answer 29

● A cone with a wire wrapped around it is connected to an
a.c power supply and is placed in a permanent
magnetic field
● When current flows through the wire, it creates a
second magnetic field, which interacts with the
permanent field
● This produces a force which causes the cone to vibrate

Question 30

How is the pitch of the sound from a
loudspeaker changed?

Answer 30

● The frequency of the a.c current is
altered
● This creates a different frequency of
vibration in the cone